Acacia dealbata (silver wattle) is similar but has greenish-grey leaves and the rachis presents glands at the junction of each pinnae pair; the flowers are of a brighter yellow and more precocious in the seasonal cycle.

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left – A. mearnsii right – A. dealbata

Characteristics that aid invasion

It reproduces by seed; it produces many seeds that remain viable in the ground for more than 50 years. The seeds are dispersed by wind, animals, or water. Germination is stimulated by fire.

The species also propagates vegetatively, sprouting vigorously from stump and roots.

It presents a relatively limited distribution area in mainland Portugal.

Impacts on ecossystems

It forms dense populations inhibiting the development of native vegetation. In Portugal, it is not one of the most dispersed species, being known few (when compared with A. dealbata, A. melanoxylon or A. longifolia) situations where these levels of impact are verified.

It produces a lot of nitrogen-rich litter, which promotes soil change.

Controlling an invasive species demands a well-planned management, which includes the determination of the invaded area, identifying the causes of invasion, assessing the impacts, defining the intervention priorities, selecting the adequate control methodologies and their application. Afterwards it is fundamental to monitor the efficiency of the methodologies and recuperation of the intervened area as to perform, whenever necessary, the follow-up control.

The control methodologies used for Acacia mearnsii include:

Physical control

Hand pulling: preferential methodology for seedlings and small plants. When in more compacted substrates, pulling should be made during the rainy season as to facilitate the removal of the root system. It should be guaranteed that no main roots are left in the ground.

Cutting with brushcutter: preferential methodology for plants resulting from the germination that are still very small. It should just be applied on warm days as long as the security conditions are respected.

Physical + chemical control

Cut stump method: Preferential methodology for adult plants. Cut the trunk as close to the ground as possible and immediately (in the following seconds) apply herbicide (active substance: glyphosate) to the cut stump. Should latter on sprouting occur, these sprouts should be immediately eliminated through cutting, pulling or foliar application of herbicide (active substance: glyphosate); up to 25 to 50 cm high. Shoots of larger dimensions (from 2-3 cm diameter) may be ring-barked or else should be repeated the initial methodology (cut stump method).

Chemical control

Foliar application of herbicide: over recent sprouts (25-50 cm tall) or when high germination rates occur. Spray with herbicide (active substance: glyphosate) limiting as much as possible its application to the target species.

Stem injection: aplica-se a plantas adultas. Apply the herbicide directly on the vascular system by drilling holes (with a drill) 10 cm deep around the trunk and in each hole immediately inject (in the following seconds) the herbicide (1 ml) with a squirt bottle. The holes should be made at a height most comfortable to the operator, in a 45º angle (to avoid the herbicide’s runoff) and in intervals of 5-10 cm between them. The number of holes to make depends on the plant’s diameter.

Biological control

The weevil Melanterius maculatus Lea (Coleoptera: Curculionidae) has been used with success in South Africa. This species feeds off seeds of A. mearnsii, causing a reduction on the number of seeds in some areas, although the destruction level of the seeds in not yet very high.

The weevil Dasineura rubiformis Rübsaamen (Diptera: Cecidomyiidae) has been used with success in South Africa. This species forms galls on the floral buds of A. mearnsii inhibiting the formation of seeds.

These agents have not yet been tested in Portugal as to verify its safety relatively to native species, so its use has not yet constituted an alternative in our country.

Prescribed fire

It may be strategically used to favour germination of the seed bank, e.g., after the control of adult individuals (with the adequate management of the resulting biomass) and the subsequent elimination of seedlings. This method provides an advantageous reduction of the seed bank, both by destroying part of the seeds and by stimulating the germination of the remainders.

Visit the webpage How to Control for additional and more detailed information about the correct application of these methodologies.

Agricultural Research Council – Plant Protection Research Institute – Weed Research Division (2014) Management of invasive alien plants: A list of biocontrol agents released against invasive alien plants in South Africa. Available: http://www.arc.agric.za/arc-ppri/Documents/WebAgentsreleased.pdf [Retrieved 03/03/2014].

Invasive Plants

Many ecosystems in Portugal are deeply affected by invasive species, either animal or plants. This means considerable economical losses, huge impacts on biodiversity, changes in the ecosystems services and even public health issues.

Our goal is to explain this problem, educating not only the common citizen but also specialized technicians to recognize and control invasive species.